1. Field of the Invention
The present invention relates to an optical imaging device which allows fluorescence observation in which excitation light is irradiated and fluorescence is received from the subject.
2. Description of the Related Art
Endoscope apparatuses have been widely used in medical and other fields. Endoscope apparatuses in the medical field in particular are used for the inspection and observation of a living body, which is the subject.
Such endoscopic observation includes not only normal visible light observation, but also fluorescence observation in which excitation lights are irradiated onto a living body, and fluorescence from a lesioned part is received and converted into an image. To perform this fluorescence observation, a fluorescent substance, such as nematoporplyrin which has an affinity with a lesioned part, such as cancer, is administered into the body of the patient. After a predetermined time elapses after administering the fluorescent substance, excitation lights are irradiated onto the living body, than the fluorescence emitted from the fluorescent substance accumulated in the lesioned part is received and generated into a fluorescent image, and based on this fluorescent image, the status of the lesioned part is judged.
Examples of an endoscope apparatus as an optical imaging device that can acquire such a fluorescent image are disclosed in Japanese Patent Application Laid-Open No. H7-155285, No. H8-224208, No. H11-244220 and No. 2005-58618.
The endoscope apparatuses disclosed in the above mentioned Japanese Patent Application Laid-Open No. H7-155285 and No. H8-224208 are configured such that an optical filter for shielding lights other than fluorescence in the return lights from a subject, which receives irradiated excitation lights, is installed in the previous stage of an image capturing element, so as to acquire the fluorescent image.
The endoscope apparatus disclosed in the above mentioned Japanese Patent Application Laid-Open No. H11-244220 is configured such that a cap, having an optical filter for shielding excitation light in the return lights from the subject, which receives irradiated excitation light, is installed at the distal portion of the endoscope, so as to acquire a fluorescent image.
The endoscope apparatus disclosed in the above mentioned Japanese Patent Application Laid-Open No. 2005-58618 is configured such that a desired cap, out of a cap having an optical filter for transmitting only excitation lights and a cap having an optical filter for shielding only the excitation lights, is installed at the distal portion of the endoscope, and a fluorescent image is acquired when the optical filter for transmitting only the excitation lights is installed at the distal portion.
On the other hand, in Japanese Patent Application Laid-Open No. 2004-294109, for example, a Raman scattering measurement device for measuring Raman scattering lights from the subject is disclosed. This Raman scattering measurement device is configured such that an optical filter for decreasing the Raman scattering lights, generated in the excitation light path, is installed at the tip of the probe.
In these conventional endoscope apparatuses as optical imaging devices, optical elements constructing the illumination light path, such as the lenses in the light source device, light guide and illumination lenses in the insertion section, and the adhesive securing these elements, may generate a slight amount of fluorescence or Raman scattering lights.
In such a case, in a conventional endoscope apparatus, the fluorescence or Raman scattering lights from the illumination light path are mixed into illumination lights which are irradiating the subject as excitation lights, reflected by the subject and enter the endoscope apparatus. If the fluorescence or Raman scattering lights from the illumination light path are included in the transmission wavelength band of the optical filter, in a conventional endoscope apparatus, these fluorescence and Raman scattering lights from the illumination light path are captured by the image capturing element along with the fluorescence generated by the subject.
Particularly, in the case when the positional relationship of the illumination light, subject and light receiving optical system is the positional relationship where the portions satisfy regular reflection conditions, the above mentioned fluorescence and Raman scattering lights from the illumination light path generate brighter images, which makes it difficult to identify whether the light is from fluorescence which comes from the subject or fluorescence or Raman scattering lights which comes from the illumination light path, and interferes with smooth observation.
Generally the intensity of fluorescence generated from the subject is extremely small, compared with the intensity of normal reflected light. Therefore in a conventional endoscope apparatus, it may become difficult to detect only fluorescence which comes from the subject if the reflected light of the fluorescence and Raman scattering lights mix in.
The Raman scattering lights measurement device according to the above mentioned Japanese Patent Application Laid-Open No. 2004-294109, on the other hand, is a device for measuring the spectrum intensity of the Raman scattering lights from the subject (in other words, a device for one-dimensionally measuring the Raman scattering lights), and is not intended to measure fluorescence and white lights other than Raman scattering lights, and particularly is not intended to perform normal endoscopic observation and fluorescent image observation by acquiring two-dimensional images. Therefore this Raman scattering lights measurement device cannot perform normal endoscopic observation and fluorescent image observation simultaneously.
In the case of the endoscope apparatus according to the above mentioned Japanese Patent Application Laid-Open No. 2005-58618, when the cap is attached, lights other than excitation lights are blocked at the distal end of the endoscope, so both normal endoscopic observation and fluorescent image observation cannot be performed in this status. In order to perform both normal endoscopic observation and fluorescent image observation, the endoscope must be extracted from the subject once, the cap is removed, then the endoscope is inserted again into the subject for observation. Therefore this endoscope apparatus is not intended to observe a white reflected light image and a fluorescent image approximately at the same time.